Syringes which can be used for mixing an active pharmaceutical ingredient with a liquid diluent, and subsequently delivering the mixed drug are known. One problem with the previous syringes is that the construction allowing the active pharmaceutical ingredient to be mixed with the liquid diluent, creates one or more cavities inside the syringe, where mixed drug is trapped during delivery of the mixed drug. Thereby part of the mixed drug is left inside the syringe, and is therefore not delivered from the syringe.
Another problem with the previous syringes is that, in the case that the active pharmaceutical ingredient is in the form of a lyophilized drug, the lyophilized drug must be prepared separately and subsequently introduced into the syringe. This adds to the manufacturing costs and causes an increased risk of contamination of the drug.
U.S. Pat. No. 5,599,312 discloses a syringe for simultaneous injection of plural medicines, or for injection of solutions of solid medicine. Different kinds of injection agents are accommodated in chamber formed separately in a cylinder, without being previously mixed.
U.S. Pat. No. 4,354,768 discloses a multiple barrel hypodermic syringe for mixing materials contained in the barrels prior to use. The syringe comprises a lower barrel for containing a sterile material such as a lyophilizable product, and an upper barrel containing a liquid diluent.